On Tue, Sep 4, 2012 at 7:38 PM, Steven Desjardins <[email protected]> wrote: > You could do a better job with many aspects of this camera. Maybe low > light is a sensor problem?
A standard Bayer mosaic sensor is a planar surface with a filter array on top of it. This means that the light at each of the photosites for all three colors is essentially equal, minus the amount that the particular color filter absorbs for each photosite. A Fovean sensor stacks three photosites in each pixel location on the sensor, with a color filter between them. I don't know precisely how they order the stack, but it would make sense to order it blue, green, red since short wavelengths are more easily absorbed than longer wavelengths. But what this means is that the light energy hitting the bottom layer is inevitably reduced compared to what hits the top layer. They compensate to some degree by making the three layers differentially sensitive, either by adjusting the signal amplification or by staggering the photosite sizings, I don't know. But what this means is that for a given amount of light energy per unit area falling on the sensor plane, a Fovean sensor has to work harder to achieve the same signal to noise characteristic than a Bayer matrix sensor. The difference is that a Fovean sensor is acquiring R, G, and B values at each pixel position, producing a non-interpolated chroma resolution at the same pixel resolution, where a Bayer mosaic takes a minimum of an 8x8 pixel array in a GRBG/RBGG/BGGR row*column (or similar ordering) to resolve each pixel's position and RGB value by interpolation. The article makes a big deal of the Fovean design not needing an AA filter to combat chroma irregularities due to the interpolation of pixel position. Well, as pixel density increases, the need for an AA filter to minimize chroma irregularities reduces such that with today's sensors the spatial resolution is very nearly identical to the Fovean sensor's capabilities at the same single-layer resolution. AA filters do more than simply minimize chroma irregularities ... they also minimize moire artifacts, the effect of discrete line crossings on a cartesian grid when the cell size of the grid is close to the width of the line. Again, as grid cell size decreases, the tendency to moire also decreases. All engineering solutions to the problem of obtaining enough color information to accurately characterize the incoming light are tradeoffs. Fovean technology means more complex to manufacture, multi-layer sensors, which have known plusses and minuses compared to Bayer mosaic sensors. My feeling is that the quality of Bayer mosaic sensor technology is such that for practical purposes, the Fovean design is mostly irrelevant except for some very critical color niche market uses. If the cost of making Fovean sensors were to drop, and a solution to the multi-layer light absorbtion issue resolved, it might stand a chance of becoming more popular than a Bayer mosaic design ... as then there would be more demand for the sensors and the price would drop further by the scaling effect of large volume manufacturing. -- Godfrey godfreydigiorgi.posterous.com -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
